"Keith Willshaw" wrote in message
...

"breyfogle" wrote in message
...
One of the factors limiting installed thrust is the ability of the duct
to
flow a maximum amount of air mass. I don't see any particular reason
why
a
different engine (optimized for a different Mach/Altitude) might not be
able
to produce more thrust when installed in the same nacelle, flowing the
same
mass of air. I'm not an engine person but seems like increasing the
compression ratio, changing the bypass ratio, increasing the turbine
temp
and increasing the fuel flow might all increase the thrust level for a
given
mass flow rate. Certainly, not every turbofan engine produces the same
thrust when flowing the same mass of air.


The problem is that the flow regime for subsonic flight is entirely
different than for supersonic flight.

The bottom line is that turbofan engines cant cope with
supersonic flow so above Mach 1 you need to slow
the flow. Trouble is this makes it inefficient at subsonic
speeds. To get round this some aircraft use variable inlet
geometries but this conflicts with stealth requirements.

The B-1A had the variable geometry required for supersonic
flight, the B-1B does not. You'd need to redesign the entire
inlet system to provide high supersonic performance.

That's certainly possible and even for a fixed inlet. If the inlet is
optimized for M2, then off design point operation may suffer somewhat but
Boeing is suggesting a supercruiser bomber in any case.